The effect still exists in some way in later version windows like the Windows Volume Mixer will freeze up or won't open if you have an application stopped at a breakpoint. I think it gets stuck waiting for a reply from something like WM_GETICON that it would have to send to top-level windows.

A single application blocked on a reply is very different from all applications halting because someone won't yield in a cooperative multitasking environment.

I would also say that anyone who sends a message to all top-level windows should use SendMessageCallback or similar so they can handle a reply asynchronously.